Perforation acoustic muffler assembly and method of reducing noise transmission through objects

ABSTRACT

A noise attenuation system is disclosed for use in a structure having a recessed fixture mounted therein or other unit which creates a hole in the structure in which it is secured, such as a ceiling. The noise attenuation system is constructed to permit the absorption of noise emitted into the structure from the mechanism. The noise attenuation includes a noise absorbing muffler positioned within the structure in an area substantially surrounding the mechanism. The noise absorbing layer includes an outer barrier layer that limits the passage of sound waves emitted from the mechanism therethrough. The noise absorbing muffler further includes a noise absorbing layer positioned adjacent the outer barrier layer. The noise absorbing layer absorbs a predetermined amount of sounds waves emitted from the recessed fixture. Additionally, an optional noise absorbing layer, or equivalent decoupling material can be included to decouple the barrier from the structure for low frequency noises.

This application is a continuation-in-part of U.S. application Ser. No.11/017,642, filed Dec. 22, 2004, which, in turn, is based on and derivesthe benefit of the filing date of U.S. Provisional Patent ApplicationNo. 60/530,981, filed Dec. 22, 2003. The contents of both of theseapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system for attenuating noise. Inparticular, the present invention relates to a system for attenuatingnoise that may be emitted from a room through a hole or opening.Additionally, the invention can attenuate noise when the opening housesany low STC object that cannot be completely enclosed, such as arecessed light fixture. The present invention further relates to amethodology for attenuating noise from a room that contains at least onehole or opening for receiving a low STC object that cannot be completelyenclosed, such as a recessed light fixture or other mechanism.

2. Description of Related Art

Hearing noises such as for example, footsteps, speech, music orenvironmental sounds from adjacent rooms, upper floors, pipes, outsidethe dwelling or adjacent dwellings is something that many peopleexperience on a daily basis. At a minimum, it can be distracting. Manyspend large sums of money to reduce the overall transmission of soundinto and/or through their dwellings in order to create quietersurroundings. Various sound insulating techniques exist to significantlyreduce and/or limit the transmission of sound through the walls,ceilings and other objects contained in today's commercial andresidential buildings. A great deal of attention is paid to theconfiguration of the walls, floors and ceilings and the materialsforming the same to provide for high transmission loss, which minimizesthe transmission of noise from one room or space to another.

The configuration and the materials are rated by its STC. STC stands for“sound transmission class” and is a single number rating derived frommeasured values of sound transmission loss in accordance with theAmerican Society for Testing and Materials (ASTM) E90 standards. Thetransmission loss through an object is a measure of its effectiveness inpreventing the sound power incident on one side of the object from beingtransmitted through it and radiated on the other side. The STC providesa single number estimate of an object's performance for certain commonsound reduction applications.

Typically, ceilings and walls have openings and/or holes formed thereinto receive various devices including electrical outlets, air ducts,lighting, speakers, etc. While the walls, floors and ceilings can beadequately insulated to limit noise transmission, these openings have anadverse impact on the transmission loss. As such, noise can enter theroom or space through the opening and the device mounted therein.

SUMMARY OF THE INVENTION

In response to the foregoing challenges, applicant has developed aninnovative noise attenuation system for use in a structure having a holefor some type of mechanism, such as a recessed light fixture mountedtherein, which cannot be addressed with a complete acoustic enclosure,due to required air flow for heat dissipation, or a needed opening, suchas when a large quantity of wires is required. The noise attenuationsystem is constructed to permit the absorption of noise emitted into thestructure from the mechanism such that the transmission loss of thestructure is not adversely impacted by the presence of the opening andthe mechanism located therein. The noise attenuation system is alsoconstructed to permit dissipation of heat from the mechanism, ifrequired. The noise attenuation includes a noise absorbing mufflerpositioned within the structure in an area substantially surrounding themechanism. The noise absorbing muffler includes an outer high STCbarrier layer that limits the passage of sound waves emitted from themechanism therethrough. The noise absorbing muffler further includes anoise absorbing layer positioned adjacent to the outer barrier layer.The noise absorbing layer absorbs a predetermined amount of sounds wavesemitted from the mechanism. An optional third layer can be secured tothe barrier layer, which would be a noise decoupling layer. This is mostcommonly used when low frequency noise may need to be decoupled from thestructure.

Applicant has also developed an innovative method for attenuating noiseemitted from a recessed light fixture mounted in an opening in astructure. The method includes determining the minimum length of a noiseattenuating muffler based upon a predetermined wavelength of a soundwave. Once the proper length of muffler is determined, the noiseattenuating muffler is located within the structure in an areasurrounding the mechanism. The noise attenuating muffler substantiallyabsorbs the sound waves emitted into structure from the recessedfixture. Thus, when the sound exits the muffler the reduction in noiseis equal to the transmission loss that would have occurred had therenever been a hole.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in conjunction with the followingdrawings in which like reference numerals designate like elements andwherein:

FIG. 1 is a perspective view illustrating the noise attenuation systemin accordance with an embodiment of the present invention whereby thenoise attenuation system is positioned between upper and lower floors;

FIG. 2 is a partial side cross-sectional view of the noise attenuationsystem in accordance with the present invention positioned betweenadjoining walls;

FIG. 3 is a cross-sectional view of the noise attenuation system takenalong the 3-3 line in FIG. 2;

FIG. 4 is a perspective view illustrating the length of the noiseattenuation system in accordance with the present invention; and

FIG. 5 is a partial perspective view illustrating a variation of thenoise attenuation system in accordance with the present invention.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

A system 10 for attenuating noise will now be described in greaterdetail in connection with FIGS. 1-4. For purpose of illustration, thesystem 10 for attenuating noise will be described in connection with theattenuation of noise associated with an opening 1 formed in a ceiling 2for receipt of a mechanism 3, as illustrated in FIG. 1. The noiseattenuation system 10 can also be used to attenuate noise associatedwith an opening formed in a wall 8, as shown in FIGS. 2 and 3. Inaccordance with the present invention, the mechanism 3 can be a recessedlight fixture or any component that is recessed in a wall or ceilingincluding but not limited to electric outlet boxes, speakers, intercoms,exhaust fans, electrical heaters, video equipment including cameras andmonitors and the like. Typically, the mechanism 3 is positioned betweena pair of joists 4 or wall studs 9. The joists 4 or studs 9 can belocated between walls 8, as shown in FIGS. 2 and 3, or between theceiling 2 and the subfloor 5, as shown in FIG. 1. The mechanism 3 can bemounted to one or both of the joists 4. It is also contemplated that themechanism 3 can be solely supported by the ceiling 2, wall 8 or by abracket (not shown) connected to one or more of the joists 4, the studs9, wall 8 or the subfloor 5. The ceiling 2 of the room or space isattached to the lower side of joists 4. The subfloor 5 of the upperfloor of an upper room is attached to the upper side of the joists 4. Aflooring material 6 is then secured to the subfloor 5. In a wallinstallation, the walls 8 are connected to the sides of the studs 9.

In order to improve the transmission loss of noise between the ceiling 2and the subfloor 5 and flooring material 6 or the walls 8, the noiseattenuating system 10 includes a noise muffler 11 that is located in thearea 7 surrounding, but usually not contacting the mechanism 3, as shownin FIGS. 1-3. The noise muffler 11 includes an outer barrier layer 12.The barrier layer 12 can be formed from a material, with a high STCbarrier. The barrier layer 12 can be formed of a loaded vinyl (e.g., aone pound per square foot loaded vinyl). The barrier layer 12 can beformed from a material having an STC rating that is equal to or greaterthan the STC rating of the wall 8, floor 5, 6 or ceiling 2 when measuredwithout the opening 1. Additionally, the material forming the barrierlayer 12 can be a non-rigid material such that the layer 12 can bemolded, shaped or manipulated to conform to the joists 4 and subfloor 5or wall 8 in the vicinity of area 7. A more rigid form of the materialcan also be used when providing noise attenuation in an area havingpredetermined dimensions. The barrier layer 12 has a suitable STC ratingsuch that any noise emitted from the mechanism 3 in the areasubstantially remains in the area 7 while the sound waves travel withinthe muffler 11.

The noise muffler 11 further includes a noise absorbing layer 13, whichis attached to or lines at least one side of the barrier layer 12, asshown in FIGS. 1 and 2. As shown in FIG. 5, the noise muffler 11 caninclude a pair of noise absorbing layers 13, which are located onopposing sides of the barrier layer 13. The second noise absorbing layercan function as a decoupler for potential low frequency noises. Thesound waves emitted from the mechanism 3 are absorbed by the noiseabsorbing layer 13 before it exits the muffler 11. With such aconstruction, a suitable transmission loss is achieved. The noiseabsorbing layer 13 is preferably a high NRC rated material, where “NRC”stands for noise reduction coefficient and represents the average amountof sound absorbed by the material. The NRC rating typically ranges from0.01 to 1.0. NRC ratings above 1 (e.g., 1.03) are also possible. Thehigher NRC rating, the greater the sound absorption. The noise absorbinglayer 13 is chosen based upon the characteristics of the particularmechanism 3. Various materials are contemplated. In particular, thematerial forming the layer 13 is chosen for its sound absorbingqualities and its ability to withstand any heat emitted from themechanism 3. As such, the material forming layer 13 for noiseattenuation of a recessed stereo speaker can differ from the materialused for noise attenuation of a recessed lighting fixture 3. Fiberglassand glass wool are considered to be suitable materials for the noiseabsorbing layer 13 for their sound absorbing and fire resistantqualities. The layer 13 may also be formed from a closely woventextile-like material formed from any suitable material provided thematerial has suitable sound absorbing properties and withstands apredetermined temperature. Additionally, it is preferable that the noiseabsorbing layer 13 be formed from a class A fire rated material. Asuitable adhesive can be used to secure the noise absorbing layer 13 tothe barrier layer 12. When multiple noise absorbing layers 13 areprovided (e.g., FIG. 5), the layers can be formed from either the samematerial or a different material. Alternatively, the noise absorbinglayer 13 can be connected to the barrier layer 12 when the layers 12 and13 are secured to the joists 4 or subfloor 5 using suitable fasteners(not shown).

In the case of the stereo speaker, it is not necessary that the layer 13withstand higher temperatures; rather, it is important that the materialhave high noise or sound absorption qualities to absorb the noiseemitted into the area 7 by the speaker that may be transmitted throughthe joists 4 and the subfloor 5 and floor 6 into adjacent spaces. Thebarrier layer 12 will attenuate the noise that may be transmittedthrough the floor into the space above through the joists 4 and theceiling 2, while the noise absorbing layer 13 will absorb noise emittedinto the area 7 by the speaker. Furthermore, it is important that thematerial does not adversely affect the acoustic wave of the speaker forthe desired sound to be emitted into the space.

In contrast, the material for the layer 13 used in connection with arecessed lighting fixture must be able to withstand higher temperaturesemitted from the mechanism 3. The noise absorbing qualities of thematerial in this application are not as important because the barrierlayer 12 will provide the primary noise attenuation. The muffler 11 canbe sized to permit the dissipation of heat from the recessed fixture, ifrequired.

As shown in FIGS. 1-3, the noise muffler 11 preferably includes sides111 and 112, which extend along the joists 4 adjoining the area 7. Anupper portion 113 is positioned adjacent the subfloor 5 (FIG. 1) or wall8 (FIG. 3). The noise muffler 11 is preferably formed with open ends topermit venting. The noise muffler 11 can also include ends, not shown,when heat venting is not required such as for speaker enclosures andelectric outlets, which extend between the joists 4 from the subfloors 5to the ceiling. The ends, however, are not necessary if the length ofthe muffler is long enough, because the noise absorbing layer 13substantially absorbs the sound waves before the sound waves can exitthe ends of the muffler 11. The muffler 11 can provide a noise absorbingbarrier having an STC rating that is equal to or greater than theceiling and surrounding structure or wall and surrounding structuredepending on the placement of the mechanism 3. As an example, themuffler 11 would travel from the ceiling up the joist 4 along thesubfloor 5 above and down the other joist 4 to the ceiling 2 attached tothe adjacent joist 4. As shown in FIG. 1, the muffler 11 surrounds themechanism 3. The muffler 11 is intended to contain the noise generatedfrom the mechanism 3 and/or transmitted through the walls, ceilings,joists, studs and floors of adjacent spaces thus creating a situationwhere the energy of the acoustic wave is forced to travel through themuffler 11. The muffler 11 is sized such that as the sound waves travelwithin the muffler 11, the sound waves are substantially absorbed by thelayer 13 such that the noise is absorbed by the layer 13 before exitingthe muffler 11.

The size of the muffler 11 may vary according to the particular noiseattenuation application. The size of the muffler 11 is determined basedupon several parameters including, but not limited to the heat generatedfrom the mechanism 3 such that proper ventilation can be provided, thefrequency of the noise to be contained by the muffler 11, the amount oftransmission loss required, and the material used to form the layer 13.The number of fixtures 3 placed in a particular area will also impactthe size of the muffler 11. For example, the number of recessed lightswhich may be located in a linear arrangement such that they arepositioned between the same two joists 4 will impact the size of themuffler 11. The muffler 11 may be sized to extend the length of thejoists 4 such that a single muffler 11 is provided for noise attenuationand proper ventilation.

Whatever the absorbing material chosen for the layer 13, it willattenuate the acoustic energy of the noise source (i.e., the fixture13). Since absorbers have a known noise absorption in a specificfrequency, the length of the muffler 11 is to be governed by thefrequency of concern, for example, substantially the lowest frequency ofthe noise, and the material used. The length is determined such that thenoise emitted from the mechanism 3 is substantially absorbed by themuffler 11 before exiting the muffler 11. The length of the noisemuffler 11 can be determined based upon a determination of thewavelength λ of the noise (e.g. substantially the lowest frequency ofthe noise). The wavelength λ is determined based upon the velocity ofthe sound waves v_(W) and the frequency f of the noise where:λ=v _(W) /fAs shown in FIG. 4, the minimum length of the muffler 11 is β where:β=2λ/NRCThe NRC rating is chosen based upon the material forming layer 13 at agiven frequency f.

Example 1

The frequency f of concern is 500 Hz. The velocity of the sound wavev_(w) is 1100 ft/sec. Using this information, the approximate desiredlength of the muffler 11 can be determined.λ=1100 ft/sec/500 Hz=2.2 ftThe NRC coefficient for a material for using in absorbing sound waveswith a frequency f of 500 Hz is 0.85.β=2λ/NRC=2(2.2 ft)/0.85=5.2 ftThe minimum length of the muffler 11 is approximately 5.2 ft with themechanism 3 being located approximately in the center of the muffler 11(i.e., ½β as shown in FIG. 4). This determined minimum length of themuffler 11 will provide adequate noise attenuation whereby the soundwaves will be absorbed prior to exiting the muffler 11 and can providesufficient space to permit ventilation of the mechanism 3 anddissipation of any heat emitted from the mechanism 3.

Example 2

The frequency f of concern is 125 Hz. The velocity of the sound wavev_(w) is 1000 ft/sec. Using this information, the approximate length ofthe muffler 11 can be determined.λ=1100 ft/sec/125 Hz=8.8 ftThe NRC coefficient for a material for using in absorbing sound waveswith a frequency f of 125 Hz is 0.65.β=2λ/NRC=2(8.8 ft)/0.65=27 ftThe minimum length of the muffler 11 is approximately 27 ft with themechanism 3 being located approximately in the center of the muffler 11(i.e., ½ β as shown in FIG. 4). This determined length of the muffler 11will provide adequate noise attenuation whereby the sound waves will beabsorbed prior to exiting the muffler 11 and can provide sufficientspace to permit ventilation of the mechanism 3 and dissipation of anyheat emitted from the mechanism 3.

The equation for β above will result in muffler 11 absorbingsubstantially all of the noise generated by mechanism 3. However,ceiling 2, wall 8, joists 4, etc. will not block all of the noisegenerated by mechanism 3. In some applications, muffler 11 need notabsorb any more noise than the surrounding structures. In this case, theminimum length β of the muffler 11 is:β=2λ/NRC·α₁whereα₁=(T _(LNH) ·T _(LH))/T _(LNH)T_(LNH) is the transmission loss through ceiling 2, wall 8, etc. withoutopening 1. T_(LNH) is the transmission loss through ceiling 2, wall 8,etc. with opening 1.

It is intended that the noise attenuation system 10 in accordance withthe present invention may be installed during the construction phase ofthe structure or as a retrofit after construction, but during theinstallation of the fixtures 3 during for example a home or officeremodeling. The installation of the system 10 during a retrofit orremodel may require the removal of a least a portion of the wall orceiling 2 to permit insertion of the muffler 3. Additionally, anyinsulation located between the joists 4 would also have to be removed inthe area surrounding the mechanism 3, if heat ventilation is required.

It will be appreciated that numerous modifications to and departuresfrom the preferred embodiments described above will occur to thosehaving skill in the art. The present invention is not intended to belimited to sound insulation between the floor and ceiling of astructure, rather, the system 10 can be used between walls or in anystructure where sound insulation is desired. Furthermore, theterminology fixture is not intended to be limited to recessed lighting;rather, the terminology fixture may include any component that may bemounted in a recess or hole in a wall, ceiling or other structure.Furthermore, the muffler 11 can be used in any application where it isdesirable to increase transmission loss through the recessed fixtureand/or provided ventilation of the recessed fixture to permitdissipation of heat from the recessed fixture when necessary, or just anopening for such items as extensive wiring. It is also contemplated thatthe noise absorbing layer 13 can be formed from one or more layers whichtogether form the layer 13. Thus, it is intended that the presentinvention covers the modifications and variations of the invention,provided they come within the scope of the appended claims and theirequivalents.

1. A noise attenuation system disposed in a structure including a wallor ceiling, the wall or ceiling including a board having an exposedsurface and an opposite surface, comprising: a heat-generating objectrequiring air flow for heat dissipation disposed in the structure, theobject either generating sound or allowing sound to pass through; and anoise absorbing muffler positioned within the structure and forming anelongated cavity and having an edge abutting the opposite surface of theboard of the wall or ceiling, at least a portion of the object extendinginto the cavity, wherein the noise absorbing muffler comprises: an outerbarrier layer that limits the passage of sound waves therethrough; andat least one noise absorbing layer positioned adjacent the outer barrierlayer, wherein the noise absorbing layer absorbs a predetermined amountof sound waves, wherein a length of the cavity defined by the noiseabsorbing muffler is selected, based upon the substantially lowestfrequency of the noise to be absorbed, the material used for the noiseabsorbing muffler, and the materials surrounding the object, such thatthe noise absorbing layer substantially absorbs at least as much of thesound waves as does the structure surrounding the object; wherein theelongated cavity has substantially completely open ends and permits thedissipation of heat emitted from the object.
 2. The noise attenuationsystem according to claim 1, wherein the outer barrier layer has a soundtransmission class rating equal to or greater than the soundtransmission class rating of the structure.
 3. The noise attenuationsystem according to claim 2, wherein the outer barrier layer is formedfrom non-rigid loaded vinyl.
 4. The noise attenuation system accordingto claim 1, wherein the at least-one noise absorbing layer is formedfrom a fire resistant material.
 5. The noise attenuation systemaccording to claim 1, wherein the noise absorbing muffler is shaped toconform to the surrounding structure.
 6. The noise attenuation systemaccording to claim 1, wherein the at least one noise absorbing layercomprises; a first noise absorbing layer located on one side of theouter barrier layer; and a second noise absorbing layer located on anopposite side of the outer barrier layer.
 7. A method for attenuatingnoise passing through an opening in a structure including a wall orceiling including a board having an exposed surface and an oppositesurface, comprising: determining a length of a cavity havingsubstantially completely open ends defined by a noise attenuatingmuffler based upon a substantially longest wavelength of a sound wave,the material used for the noise attenuating muffler, the difference intransmission loss through the structure with and without the opening;and locating the noise attenuating muffler within the structure so thatan edge of the noise attenuating muffler abuts the opposite surface ofthe board in an area surrounding the recessed object, such that thenoise attenuating muffler substantially absorbs at least as much of thesound waves emitted from the recessed object as does the structuresurrounding the object; wherein a heat-generating object requiring airflow for heat dissipation and either generating sound or allowing soundto pass through is disposed in the structure, and the cavity formed bythe noise absorbing muffler permits the dissipation of heat emitted fromthe object.
 8. The method for attenuating noise according to claim 7,wherein the noise attenuating muffler comprises: an outer barrier layerthat limits the passage of sound waves into the structure; and a noiseabsorbing layer positioned adjacent the outer barrier layer, wherein thenoise absorbing layer absorbs a predetermined amount of sound waves. 9.The method for attenuating noise according to claim 8, furthercomprising: determining the sound transmission class rating of thestructure without the opening; and selecting a suitable material forforming the outer barrier layer that has a sound transmission classrating that is at least equal to or greater than the sound transmissionclass rating of the structure.